QObject::sender() is a slow function

I did not expect that its share of CPU usage in my app is 12.15%:

Why does it iterate over some collection? Isn’t there only one sender in a thread?

My code:

void connectElement(ElementModel* p)
{
    QObject::connect(p, &ElementModel::elementChanged, this, &TableModel::onElementChanged, Qt::UniqueConnection);
}

void onElementChanged()
{
    QObject* p_obj = sender(); //12.15% of CPU usage

    onUpdated(dynamic_cast<T*>(p_obj)->shared_from_this());
}

is called from UpdateGuard constructor:

and a similar code is called from UpdateGuard destructor

UpdateGuard total CPU usage is 13.73% + 14.45% = 28.18%. For comparison, QML binding CPU usage share is 18.95% + 8.65% = 27.6%. The total CPU usage of entire MarketModel::setPrice function is 57.42%.

Another example is WalletModel::savePrice:

QObject::senderSignalIndex() also iterates over this collection:

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